Відео

The "sound" shouldn't improve much by larger caps (new caps might help filter out hum better though). On voltage rating, you can go as high as you want, but try to stick within 120% of the original capacitance values, any higher and the inrush currents when powering on can become an issue. When I replace these, I generally look for caps with the same diameter and leg spacing, slightly higher voltage rating, similar capacitance (100-120% of original rating) and the highest temperature rating I can find. Better capacitance tolerance isn't worth paying extra for though, +/- 20% is good enough for big filter capacitors.

Try filming something you've done hundreds of times and narrating it at the same time yourself, you might be surprised 🤣 but yeah, I'm not pleased with this video, I might redo it where you can actually see what I'm doing.

Sadly I no longer have this amp, so I can't measure it. However, if the amp makes a clicking sound or makes no sound at all, check if the power mosfets are shorted, they blow quite often. Or is there no voltage present on the main capacitors, check if the power supply switching mosfets are dead or the driver IC is dead. The voltage on the main caps should be around +80 and -80 volts, 150 volts on the PF500

Yeah, seems so, but I'm still unsure what made it pop like that as I can't find any other problem with the amp, and even shorted FETs in the power amp doesn't cause that fuse to pop as the power supply is very well protected. My only theory is that someone selected the wrong line voltage.

Hmm, I seem to remember that the rails were around 80 volts on mine as well. Could it be a problem with the preamp or that the pad is engaged?

@@GrumpytechieNet Humm thanks. It is weird. I think +-80v is suspicious be because of the frying of these R98/R94. everytime they are in. Why would schematic says it is +55? ... Maybe its the revision difference. the pad is the first thing i checked. It is ok. I will check the preamp section now. thanks for the tips

Surprisingly smooth, a bit less gritty than French press.

It's quite the beast, 15 kg maybe. It's a push-pull off memory serves.

Yupp, they work if you need to make 20 cables in one go, and you never change brand of cable. For one-off cables I generally use a razor.

@@GrumpytechieNet Good point. I can't say I've ever tried tweaking them for reliable cuts on one roll of cable. Wasn't even clear, or possible, to adjust the couple I have tried. Good to know if I ever have to, though.

@@radellaf Almost every coax stripper I've used have little set screws for adjusting the blades, as the tolerances are so small that just switching brand of cable can make it cut too deep or too shallow.

Since these amps have a switch-mode power supply internally, they can behave a bit weird, in an upcoming video I have a PF500 that did start even though one of the output mosfets were completely burned.

@@GrumpytechieNet the tech said the power section will have to be repaired, so I will have to spend some cash. Well, at least it can be repaired.

@@ZombieBath They are quite sturdily built, so I'd expect only a few components being burned. It's hard to say though, repairs like that are usually a matter of replacing failed components, see if it works, finding more components to replace etc. So it can take some time to fix.

Could be either or a shorted power transformer. Start checking resistance between power and ground, working from the power cable towards the mosfets. That way you work towards the short. Remember to also flick the power switch on and off to see if the problem is before or after the switch. How large is the fuse in the plug, 13A?

@@GrumpytechieNet Thanks for the reply. The transformer is ok because I tested it disconnected from the circuit and the fuse doesn't blow. The fuse is 1.6A as indicated on the back. I'll try to check the rest of the circuit over the weekend.

From what I remember I went with the formula 60g/1000g water. French press grind is approx what you want for it.

Seems a bit odd to be honest, so they get hot with the amp just sitting idling, turned on with no input signal? The bent aluminium plate that function as a heat sink for the transistors is supposed to be bolted to the chassis with thermal compound in between it and the chassis. Maybe the old compound had dried up over the years?

@@GrumpytechieNet Thanks for the quick response. Idling, there is a little heat. Pushed hard, they heat up. I believe they are rated at 150C. TIP31C and TIP32C have their own, individual L-shaped heat sinks, mounted on the PCB. I cleaned off all the old compound and liberally applied new throughout. R12, R13, R30 and R31 also run hot. I've played it now for a week and so far, it's working. I'm thinking maybe it's normal. Hopefully, the larger heat sinks will give it longevity. Maybe that's why they don't make this model anymore.

@@eddiegarcia3202 I'll check the heat levels in mine, I'm still in the middle of replacing some pots!

@@GrumpytechieNet Thank you. Great channel, BTW!

@@GrumpytechieNet Did you ever check the heat levels on the transistors? So far the larger heat sinks on mine seem to be working. The heat sinks are hotter to the touch than the transistors themselves!

I would imagine that alginate can't take the temperature.

You're quite right, but I'd still recommend a resistance test as it tells you if you accidentally shorted the cable making it, and if you have a DC-shorted antenna at the other end of a longer cable it also tells you of you have excessive resistance. VNAs are superior, but you might not always have one with you.

Check the link in the description, he has a series on how to build it and explains how it works. Essentially it's just light bulbs in parallel with each other in series with the load. Each bulb has a switch in series with it, and the bypass is just a switch without a bulb in parallel.

@@GrumpytechieNet Thanks 👍

No worries mate! The components are from Mouser, they have quite a good policy regarding free shipping including import duties. I'm actually working on a third part on this video, as the pots never cleaned up properly, so I'd get the pots as well while you're in there.

@@GrumpytechieNet thanks for that I'll look out for your next video. I'm also missing 2 knobs, no idea where to get them from!

@@GrumpytechieNet Further from my previous comment, my amp was water damaged so much that it had rusted the bolts holding the board to the cabinet so couldnt get it out, another one came up on ebay for £50 so I've bought that one, seems perfect apart from a crackly volume pot, as it's over 20 years old would you recommend replacing the caps as a matter of course? And as a thank you for this video I have 3 knobs which you can have, if you can send me your email address I'll contact you and post them to you. Thanks Sean

@@seanf42 I'd say replace them all while you're at it, they aren't that many nor very expensive. Be prepared that some of the pots might be shot as well, I had to replace the volume 1 Meg as well.

Not much worse than a French press

That's a good point, but they should work just as well with any suitable PVC/Nylon tubing, as long as the outer diameter is the same.

No idea, but I'd guess around 8 ohms.

It had some personal information on it and I forgot about it while shooting the video! 😁

No worries mate, I don't do these every day (or even every week), so I'm not fast under normal circumstances, and as soon as you try to show something it's instantly a lot harder. :)